Lecture: Ancient civilizations: Narrator: Listen to part of a lecture in an ancient history class. Professor: Alright, so like many ancient civilizations, the Romans helped develop important technologies. Today, we're going to focus on one particular technological development that was as artistic as pleasing to the eye as it was functional. I'm talking about their water distribution system, also known as aqueducts. Aqueducts are channels that lead water from its source like an underground spring to another location, usually a city. This is important because, well, cities need large water supplies and the Roman Empire had a lot of large cities. Remember, it was one of the largest ancient empires. Without the aqueducts, which were built through the Empire, well, the Roman Empire probably wouldn't have spread so far nor had such highly populated cities. Take the city of Rome, the capital of the Roman Empire. It's estimated that it had between 500,000 and 1,000,000 residents. To supply all these people with water was a major engineering achievement. Over a period of several hundred years, 11 aqueducts were built to bring water to Rome from as far away as 90 kilometers. And some estimate that they delivered about 1,000 liters of water per person per day. Well, that amount of water would have been impossible to find in Rome in the area immediately surrounding it. Plus, any water source in or close to the city would quickly become polluted. I mean, we're talking about half a million people or more. Speaking of all those people, aqueducts also helped keep ancient Rome clean. The constant overflow of water would flush the city's trash out. So how were aqueducts built? Well, first they had to find a fresh water source, usually an underground spring. Once a spring was located and tested for quality, engineers would find the best dip. This means that the most gradual, gentle gradient would slope downwards towards the city. That means the source had to be higher, at a higher elevation, than the city it was serving. Since the system of aqueducts relied entirely on gravity to lead the water down through the pipes and channels, the Roman aqueducts were built out of pipes, generally lead or earthenware pipes, which made up the bulk of an aqueduct. Some of those trenches were dug and the pipes were laid and covered. This way, most of an aqueduct was hidden and the land above could still be utilized. Also, tunnels were less vulnerable to enemies and so one of the first aqueducts was built entirely underground. Some of these tunnels, specifically the ones deep under the mountains, are such amazing engineering achievements, it's still a mystery to us how ancient Romans went about surveying and building them. And if the landscape in some areas didn't fit the specifications needed for the aqueduct, if say there was a sharp dip, a riverbed, or a valley, then engineers built an arcade. As you can see, a Roman arcade is a series of arches. An opened concrete channel runs along the top, which kept the water at a certain level even though the land dipped down because if you lost that level it was hard to get it back up again. Arcades are what make people think of a Roman aqueduct even though the greater portion of the aqueduct system was underground. But the arcades are above ground where everyone can see them. And this is where the conjunction of engineering techniques and artistic creation comes in. The arcades were certainly beautiful. In fact, many Romans built houses overlooking the arcades because well, they're kind of like landscape art. The beauty can make us forget the purpose they serve, their practical and technological value. So it wasn't just the practical aspect of arcades that were important to Romans. And the arched arcades were obviously practical, right? Say we have to build a high structure. Building arches requires less material than building solid walls, right? And if we compare Roman aqueducts, we'll see the refinements of the Roman skills in both style and scale. Arcades, especially those that were built later, are perfect examples of the marriage of functionality and elegance, qualities that were very important to Roman architects, qualities architects still try to emulate today.